Aluminum casting method and mold

ABSTRACT

An aluminum casting method is for pouring an aluminum molten metal (12) pumped up by an electromagnetic pump (20) into a die (50). A thickness of a powder demolding agent applied to the die (50) is set to be thinner than that of a demolding agent for a gravity die casting. A temperature of the die immediately before the molten metal is poured is controlled so as to fall within a range that is between 110° C. to 250° C. A temperature of the molten metal when poured is controlled to be a value obtained by adding 20° C. to 55° C. to a liquidus-line temperature of the aluminum.

TECHNICAL FIELD

The present disclosure relates to an aluminum casting method and a die utilized for the aluminum casting method.

BACKGROUND ART

An aluminum product is obtained by melting an aluminum alloy (will be referred to as aluminum below) and pouring the aluminum molten metal in a die.

An example known aluminum product is a knuckle that is a component of a vehicle. The knuckle has a projecting portion extended radially around the axle portion. A knuckle is a component in a complicated shape.

A technology is proposed for producing a knuckle by a gravity die casting (see, for example, Patent Document 1).

According to the gravity die casting disclosed in Patent Document 1, a molten metal is poured in a pouring gate opened upwardly. The molten metal flows down through a sprue runner by gravity, and changes the direction horizontally. The molten metal having undergone the direction change flows in one cavity, a cavity for an axle portion, and the other cavity in sequence, and then fills all the cavities.

Moreover, a die for casting a knuckle is proposed (see, for example, Patent Document 2 (FIG. 6)).

The technology disclosed in Patent Document 2 will be described with reference to FIG. 15 (a plan view).

As illustrated in FIG. 15, a die 100 includes a center cavity 101 to form an axle portion, a first cavity 102 extended in one side from the center cavity 101, and a second cavity 103 extended in the other side from the center cavity 101.

Moreover, the die 100 includes a pouring gate 104 and a sprue runner 105. The sprue runner 105 serves to connect the pouring gate 104 with the first cavity 102.

A molten metal flows in the pouring gate 104, the sprue runner 105, the first cavity 102, the center cavity 101, and the second cavity 103 in sequence.

The technologies disclosed in Patent Document 1 and in Patent Document 2 are called a gravity die casting. The gravity die casting has a remarkably low pressure of a molten metal in comparison with high-pressure casting represented by die-casting. Since the pressure of the molten metal is low, according to the gravity die casting, it is unnecessary to make a die robust and also to make a casting apparatus robust. Hence, the gravity die casting is widely in practical use.

Conversely, the gravity die casting has the following disadvantages.

Since the flow speed of a molten metal depends on the gravity, it is slow. Accordingly, when the temperature of a die is too low, the molten metal is solidified before reaching the end portion of a cavity.

In order to address this technical problem, the temperature of a molten metal is increased. Experientially, a value obtained by adding 100° C. to the liquidus-line temperature of the molten metal is set as a molten metal temperature.

By setting the temperature obtained by adding 100° C. to the liquidus-line temperature, undesired solidification can be addressed.

Although the molten metal is cooled and solidified after being poured, since the temperature of the die is high, it takes time for solidification. When it takes a time for solidification, a production time becomes long, and thus the productivity decreases.

According to the high-pressure casting like die casting, the flow speed of a molten metal is fast, and the productivity does not decrease. However, a die and a casting apparatus become expensive, which is not easily adoptable.

While the improvement of the productivity is desired, a casting method is desired which can improve the productivity without making a molten metal at high pressure.

Next, the die 100 will be described.

In FIG. 15, a molten metal flows in the pouring gate 104, the sprue runner 105, the first cavity 102, the center cavity 101, and the second cavity 103.

Since a distance from the pouring gate 104 to the end portion of the second cavity 103 (an upper right corner in the figure) is long, a molten metal pouring time becomes long. When the molten metal pouring time becomes long, a casting time becomes also long and thus the productivity decreases.

Moreover, it is necessary to increase the molten metal temperature in such a way that the molten metal can reach the end portion of the second cavity 103. This is because when the molten metal temperature is too low, the molten metal is solidified and cannot flow up to the end portion.

When, however, the molten metal temperature is high, a solidification time becomes long, and thus the productivity decreases.

While the improvement of the productivity is desired, it is desired to reduce the distance from the pouring gate to the end portion of the second cavity.

In order to meet such desires, the inventors of the present disclosure examined to move the pouring gate 104 to an intermediate position between the first cavity 102 and the second cavity 103. This is because the distance from the pouring gate 104 to the end portion of the second cavity 103 becomes substantially half. With reference to FIG. 16 and FIG. 17, the details of this examination will be described in detail.

As illustrated in FIG. 16, a conventional knuckle cast 110 includes a center portion 112 that has an axle hole 111, a first projecting portion 113 that is projected from the center portion 112, a second projecting portion 114 that is protruding from the center portion 112, and a third projecting portion 115 that is projected from the center portion 112.

As illustrated in FIG. 17, a die 120 for casting the knuckle cast 110 in such a shape includes a center cavity 121, a first cavity 122, a second cavity 123, and a column portion 124 projected so as to form the axle hole 111, and also includes a pouring gate 125 and a sprue runner 126 at the bottom surface.

This reduces the distance from the pouring gate 125 to the end portion of the second cavity 123, and thus the molten metal pouring time can be reduced, thereby improving the productivity.

Meanwhile, a molten metal 127 that flows through the sprue runner 126 collides a flat top surface 128 of the column portion 124. Next, the flowing direction is changed by 90 degrees to the left side or to the right side. That is, the flowing direction keenly changes. The collision and the keen change of the flowing direction causes the flow of the molten metal 127 to be into turbulence. Such a turbulence causes casting defects like trapping a gas.

Even if the productivity is improved, it is not appropriate to cause any casting defects.

Accordingly, there is a desire for a die that can reduce a distance from a pouring gate to the end portion of a second cavity without a casting defect.

CITATION LIST Patent Literatures

-   Patent Document 1: JP 2014-76450 A -   Patent Document 2: JP 2012-143788 A

SUMMARY OF INVENTION Technical Problem

An objective of the present disclosure is to provide a casting method that can improve a productivity without causing a molten metal to be high pressure, and to provide a die that is applicable to this casting method.

Solution to Problem

According to a first example embodiment of the invention, an aluminum casting method is of pouring an aluminum molten metal pumped up by an electromagnetic pump into a die,

in which a thickness of a powder demolding agent applied to the die is set to be thinner than a demolding agent for a gravity die casting,

in which a temperature of the die immediately before the molten metal is poured is controlled so as to fall within a range that is between 110° C. to 250° C., and

in which a temperature of the molten metal when poured is controlled to be a value obtained by adding 20° C. to 55° C. to a liquidus-line temperature of the aluminum.

According to a second example embodiment of the present disclosure, preferably, a die is utilized for the aluminum casting method according to the first example embodiment, and the die is for casing a cast that includes:

a center portion;

a first projecting portion projecting from the center portion; and

a second projection portion projecting from the center portion in an opposite direction to the first projecting portion,

in which the die includes:

a pouring gate provided at a bottom surface;

a main sprue runner extended upright from the pouring gate;

a first sprue runner branched from the main sprue runner;

a first cavity to which a molten metal is supplied from the first sprue runner, and which forms the first projection portion;

a second sprue runner branched from the main sprue runner; and

a second cavity to which the molten metal is supplied from the second sprue runner and which forms the second projecting portion,

in which a conical portion that protrudes into the main sprue runner is provided at an outlet of the main sprue runner, and the molten metal that passes through the main sprue runner is divided into the first sprue runner and the second sprue runner along a conical surface of the conical portion.

According to a third example embodiment of the invention, preferably, the die is according to the second example embodiment, in which:

the cast is a knuckle;

the center portion is an axle portion provided with an axle hole;

the die further includes a column portion to form the axle hole; and

the conical portion is provided at a tip of the column portion.

According to a fourth example embodiment of the invention, preferably, a die is for the aluminum casting method according to the first example embodiment, and the die includes a degassing portion to discharge a gas remaining in a cavity,

in which the degassing portion is provided with a vent hole with a dimension that is between 30 μm to 80 μm.

According to a fifth example embodiment of the invention, preferably, the die is according to the fourth example embodiment, in which:

the degassing portion is a cylindrical body fitted in the die;

the cylindrical body includes a bottom portion that faces the cavity; and

the bottom portion is provided with the vent hole.

According to a sixth example embodiment of the invention, preferably, the die is according to the fifth example embodiment, in which the vent hole is a slit with a width that is between 30 μm to 80 μm.

According to a seventh example embodiment of the invention, preferably, the die is according to the sixth example embodiment, in which a plurality of the slits is provided in the bottom portion so as to be in parallel with each other.

According to an eighth example embodiment of the invention, preferably, the die is according to the fifth example embodiment, in which the cylindrical body also serves as a product extrusion pin to separate a cast from the die.

Advantageous Effects of Invention

According to the first example embodiment of the invention, the molten metal is pumped up by the electromagnetic pump. The electromagnetic pump applies fine pressure variation to the molten metal, and this pressure variation increases the fluidity of the molten metal. According to the method of the invention, since the fluidity can be remarkably increased in comparison with the fluidity of the molten metal in gravity die casting, the temperature of the molten metal can be decreased in comparison with the gravity die casting.

Moreover, according to the method of the invention, since the fluidity can be remarkably increased in comparison with the fluidity of the molten metal in low-pressure die casting, the temperature of the die can be also decreased.

Furthermore, according to the method of the invention, since the applied demolding agent is thin, the heat from the molten metal is promptly transferred to the die, and thus the solidification time can be reduced.

Accordingly, the molten metal according to the invention completes the solidification within a remarkably short time in comparison with the gravity die casting. Since the casting time can be reduced, the productivity is improved.

That is, according to the invention, there is provided a casting method that can improve a productivity without causing a molten metal to be high pressure.

In addition, according to the invention, since the molten metal can be solidified within a short time, the solidified composition is refined. The refined composition improves a mechanical strength of a cast.

According to the second example embodiment of the invention, the conical portion is provided at the outlet of the main sprue runner, and the molten metal is branched into the first sprue runner and the second sprue runner along the conical surface of the conical portion. A change in the flow of the molten metal is made gentle. This suppresses an occurrence of casting defect.

Moreover, since the pouring gate and the main sprue runner are provided between the first cavity and the second cavity, the distance from the pouring gate to the end portion of the second cavity is reduced.

Hence, according to the invention, there is provided a die that can reduce a distance from a pouring gate to a second cavity without any casting defect.

According to the third example embodiment of the invention, the cast is a knuckle, the center portion is an axle portion provided with an axle hole, the die further includes a column portion to form the axle hole, and the conical portion is provided at a tip of the column portion.

When the product is a knuckle, the axle hole is necessary. Since the conical portion is provided at the column portion that forms the axle hole, the conical portion can easily protrude in the main sprue runner, thereby suppressing the manufacturing costs of the die.

According to the fourth example embodiment of the invention, in the die in which the aluminum molten metal pumped up by the electromagnetic pump is poured, the die is provided with the degassing portion, and the degassing portions is provided with the vent hole that has a dimension of 30 μm to 80 μm. In the case of the dimension that is 30 μm to 80 μm, the technical problem of burr can be addressed, and the degassing performance can be ensured.

Hence, according to the invention, there is provided a die the prevents a molten metal from entering a clearance for degassing when the aluminum molten metal is poured by an electromagnetic pump.

According to the fifth example embodiment of the invention, the degassing portion is a cylindrical body fitted in the die, and the bottom portion of the cylindrical body is provided with the vent hole.

Since a die is large and heavy, it is not easy to directly form a clearance in the die. In contrast, according to the invention, the clearance is provided in the cylindrical body that is separated from the die. Since the cylindrical body is small and lightweight, the formation process of the clearance is facilitated.

According to the sixth example embodiment of the invention, the vent hole is a slit. Since the slit is an elongated hole, the opening area can be achieved. Moreover, the slit can be easily formed by a wire discharging and processing machine.

According to the seventh example embodiment of the invention, since the plurality of the slits is provided, the opening area is increased, improving the degassing performance.

According to the eighth example embodiment of the invention, the cylindrical body also serves as a product extrusion pin. Since the cylindrical body accomplishes both the degassing action and the product extrusion action, the added value increases.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a fundamental diagram of a casting apparatus that executes an aluminum casting method according to the present disclosure;

FIG. 2 is a cross-sectional view of an electromagnetic pump;

FIG. 3 is an enlarged view of a part 3 in FIG. 2;

FIG. 4A is a front view of a cast, and FIG. 4B is a perspective view of a knuckle cast;

FIG. 5 is a cross-sectional view of a die, and is a cross-sectional view corresponding to a cross section taken along a line 5-5 in FIG. 4B;

FIGS. 6A to 6C are each a diagram for describing a temperature range of a die according to a comparative example and a casting time thereof;

FIGS. 7A to 7C are each a diagram for describing a temperature range of the die according to an embodiment and a casting time thereof;

FIG. 8 is a cross-sectional view of a knuckle cast immediately after being demolded;

FIG. 9 is an exploded view of the knuckle cast;

FIG. 10 is a cross-sectional view of the major portion of a movable die;

FIG. 11 is a cross-sectional view of a degassing portion;

FIG. 12 is a bottom view of the degassing portion;

FIGS. 13A and 13B are each a diagram for describing a modified example of the degassing portion, and a FIG. 13A A is a diagram illustrating radial vent holes, and FIG. 13B is a diagram illustrating fine circular holes;

FIG. 14 is a diagram for describing that a cylindrical body also serves as a product extrusion pin;

FIG. 15 is a plan view of a conventional die;

FIG. 16 is a cross-sectional view of a conventional knuckle cast; and

FIG. 17 is a cross-sectional view of a die corresponding to a conventional knuckle cast.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described below with reference to the accompanying figures.

Embodiments

As illustrated in FIG. 1, a holding furnace 10 is a furnace that is provided with heaters 11, and stores a molten metal 12 that is aluminum. The holding furnace 10 is provided with an electromagnetic pump 20. The electromagnetic pump 20 is controlled by a control unit 32.

Moreover, the molten metal 12 is heated or is kept warm by the heater 11 at a temperature that is equal to or higher than a melting point, and such a temperature is controlled by a temperature control unit 66.

According to this example, a steel frame 13 is placed on the holding furnace 10, and the electromagnetic pump 20 is supported by the steel frame 13. However, how to attach the electromagnetic pump 20 to the holding furnace 10 is optional.

Note that the holding furnace 10 is a facility that maintains the temperature of the molten metal 12 at a predetermined value. The holding furnace 10 may be a melting furnace, a tapping melting furnace, or a container like a ladle that reserves aluminum in a molten state, and is not limited to a narrowly defined holding furnace.

The detailed structure of the electromagnetic pump 20 will be described with reference to FIG. 2.

As illustrated in FIG. 2, the electromagnetic pump 20 includes a base flange 21, a molten metal guiding pipe 22 that passes completely through the base flange 21 so as to extend vertically, a core member 23 stored in the molten metal guiding pipe 22, a lower coil 24 surrounding the lower portion of the molten metal guiding pipe 22, a lower casing 25 hung by the base flange 21 so as to surround the lower coil 24, an upper coil 26 surrounding the upper portion of the molten metal guiding pipe 22, an upper casing 27 that is placed on the base flange 21 so as to surround the upper coil 26, a discharging pipe 28 that extends upwardly from the molten metal guiding pipe 22, and a molten metal level gauge 29 surrounding the discharging pipe 28.

When a current flows through the lower coil 24, the molten metal (see FIG. 1, reference numeral 12) is pulled up by the Fleming's left-hand rule.

Next, when a current flows through the upper coil 26 and no current flows through the lower coil 24, the molten metal is pulled up to the molten metal level gauge 29. This level of the molten metal level gauge 29 is a “standby level”.

Such controls are executed by the control unit (see FIG. 1, reference numeral 32).

When the current is increased, by the Fleming's left-hand rule, force increases.

When the current to the upper coil 26 is further increased, the molten metal goes over the molten metal level gauge 29, and is discharged above the discharging pipe 28. The molten metal passes through a molten metal guiding block 14 illustrated in FIG. 1, and is poured in the die 50.

Accordingly, the electromagnetic pump 20 is a pressure-applying molten metal pouring mechanism which pumps up the molten metal 12 stored in the holding furnace 10, and which supplies such molten metal to the die 50.

Note that the die 50 is provided with a heater and a water passage, and the temperature of each portion of the die 50 is always measured by the temperature control unit 66 so as to perform a temperature control that causes the measured value to be a predetermined temperature. Such a temperature control causes the temperature of the die 50 to be maintained at an appropriate temperature.

There is a pressure phenomenon peculiar to an electromagnetic action in the electromagnetic pump 20 as the pressure-applying molten metal pouring mechanism, and the inventors of the present disclosure keenly paid attention to this phenomenon. The phenomenon will be described with reference to FIG. 3.

As illustrated in FIG. 3, the molten metal 12 flows upwardly through a passage between the molten metal guiding pipe 22 and the core member 23. Magnetic fields 31 that reaches the core member 23 from an upper end 26 a of the upper coil 26 become in a curved shape so as to project upwardly. The degree of this curving changes. That is, when the power feeding frequency is 50 Hz, the degree of the curving changes at 100 Hz that is twice.

The pressure (discharge pressure) of the molten metal 12 finely varies at a fine frequency (100 Hz) due to the change (displacement) of the magnetic field 31. That is, inevitable fine pulsing motion occurs in the molten metal 12.

Next, a form of the cast 35 will be described.

As illustrated in FIG. 4A, the cast 35 includes a center portion 36, a first projecting portion 42 that projects from the center portion 36, and a second projecting portion 43 that projects, from the center portion 36, in another direction from the first projecting portion 42. Although the application of the cast 35 is optional, for example, it is applied as a knuckle cast that is a kind of a vehicular component.

As illustrated in FIG. 4B, the knuckle cast 40 that is the cast 35 includes an axle portion 41 that corresponds to the center portion 36, the first projecting portion 42 that largely projects from the axle portion 41, the second projecting portion 43 that projects from the axle portion 41 toward the opposite side, and a third projecting portion 44 that projects from the axle portion 41 in the depthwise direction of the figure. The axle portion 41 is provided with an axle hole 45 at the center.

The die 50 that is suitable for casting the knuckle cast 40 in such a form will be described with reference to FIG. 5.

As illustrated in FIG. 5, the die 50 includes a stationary die 51 and a movable die 52.

The movable die 52 is provided with a first cavity 53 to form the first projecting portion (see FIG. 4B, reference numeral 42), a second cavity 54 to form the second projecting portion (see FIG. 4B, reference numeral 43), and a third cavity 55 to form the third projecting portion (see FIG. 4B, reference numeral 44).

In addition, the movable die 52 is provided with a column portion 56 to form the axle hole (see FIG. 4 B, reference numeral 45). The column portion 56 is a pillar that has a draft angle, extends to the stationary die 51 so as to pass completely through the first to third cavities 53 to 55, and includes a conical portion 57 which becomes keen downwardly and which is provided at a tip of such a column portion.

The stationary die 51 includes a pouring gate 58 in the lower surface, includes a main sprue runner 59 extended upwardly from the pouring gate 58, and also includes a first sprue runner 61, a second sprue runner 62, and a third sprue runner 63 which are branched by the conical portion 57, and which extend along the conical portion 57. The third sprue runner 63 passes through the depthwise side in the figure relative to the conical portion 57 and the front side in the figure due to the convenience of drawing work.

The first sprue runner 61 is in communication with the first cavity 53, the second sprue runner 62 is in communication with the second cavity 54, and the third sprue runner 63 is in communication with the third cavity 55.

The conical portion 57 is formed at the outlet of the main sprue runner 59 in a shape projecting to the main sprue runner 59.

Hence, the molten metal 12 that flows from the pouring gate 58 to the main sprue runner 59 is divided by a vertex 57 a of the conical portion 57, and flows along a conical surface 57 b. Accordingly, the molten metal 12 that flows through the first sprue runner 61, the second sprue runner 62, and the third sprue runner 63 flows smoothly without a turbulence.

In the figure, reference numeral 64 indicates a boundary line between a product portion and a non-product portion, and the boundary line 64 is a line that passes through the boundary line between the conical portion 57 and the column portion 56.

Next, a molten metal that is poured in a die (see FIG. 6A, reference numeral 130) or in a die (see FIG. 7, reference numeral 50) will be described with the present disclosure (the casting method utilizing the electromagnetic pump) being compared with a conventional technology (gravity die casting).

According to the gravity die casting, a die temperature (the temperature varies depending on the portions) immediately before pouring was controlled within a range between 240° C. to 360° C. In addition, a demolding agent described with reference to FIG. 6B was applied to the die.

As illustrated in FIG. 6A, the molten metal was poured from a pouring gate 131 provided at a higher position of the die 130. The molten metal passed through a sprue runner 132 that inclines downwardly, and filled a cavity 133.

As illustrated in FIG. 6B, a demolding agent 134 had a thickness to set to 150 μm based on experiences.

Regarding the demolding agent 134, for example, black lead or ceramics were dissolved in a solvent, and were applied to the die 120 by a gun or by a brush.

As illustrated in FIG. 6C, the casting time in this condition was 80 seconds.

As described with reference to FIG. 3, when the electromagnetic pump is applied, the fluidity of the molten metal increases. In view of this technical knowledge, the inventors of the present disclosure found that even if the molten metal temperature is decreased, the molten metal can flow to the end portion of the cavity. In addition, when the molten metal temperature decreases, the die temperature immediately before pouring can be reduced.

Furthermore, since a thermal damage to the die is reduced when the molten metal temperature is decreased, the demolding agent can be made thin. In addition, since a thermal damage to the die is reduced by the high fluidity of the molten metal, the demolding agent can be also made thin.

In view of the foregoing technical knowledges, the present disclosure is derived. The details of the present disclosure will be described with reference to FIGS. 7A to 7C.

According to the casting method utilizing the electromagnetic pump, the die temperature (the temperature varies depending on the portions) immediately before pouring was controlled within the range between 120° C. to 240° C. Even under such a condition, the molten metal flowed to the end portion of the cavity without a solidification. In addition, a demolding agent illustrated in FIG. 7B was applied to the die.

As illustrated in FIG. 7A, according to the embodiment, the molten metal was poured in the die 50 by the electromagnetic pump 20.

As illustrated in FIG. 7B, the demolding agent applied was a powder demolding agent 65. Regarding the powder demolding agent 65, powders were sprayed to the die 50 by electrostatic spraying.

The powder demolding agent 65 includes, for example, powders that have primary components which are diatom earth. Since diatom earth has a large number of fine gaps thereinside, air is trapped in such gaps, thus having an excellent heat insulation performance. Even if a film thickness is thin, heat transfer from the molten metal to the die 50 can be efficiently blocked.

Because of electrostatic spraying, the adhesion force of sprayed objects at the time of spraying increases. In addition, when the sprayed objects are powders, the powders are aligned in a line on the surface of the die 50. In comparison with existing demolding agents, a prospect is obtained such that even if it is thin, a sufficient demolding performance is maintained. Hence, according to the present disclosure, a thickness Tb of the powder demolding agent 65 was set to 20 μm.

As illustrated in FIG. 7C, the molten metal temperature was decreased by 10° C. so as to be 700° C., and the die temperature (the temperature varies depending on the portions) immediately before pouring was set within a range between 120 to 240° C., and the molten metal was poured in the die 50. The casting time in this condition was 45 seconds.

Since the thickness Tb of the powder demolding agent 65 was thin, thermal migration from the molten metal to the die 50 became active, and a prospect is obtained such that the casting time can be remarkably reduced.

Hence, the inventors of the present disclosure carried out tests to be described below. In such tests, based on a presumption such that a molten metal reaches the end portion of a cavity, the molten metal temperature was decreased.

(1) Test Conditions

(1-1) Casting method: Gravity die casting or casting method utilizing an electromagnetic pump.

(1-2) Thickness of demolding agent: 150 μm or 20 μm (powders).

(1-3) Molten metal: AC4CH (aluminum alloy) that has a liquidus-line temperature which is 615° C.

(1-4) Molten metal temperature: 710° C., 700° C., 680° C., 670° C., 660° C., or 635° C.

(1-5) What is measured in the tests: Casting times

Test 01: A 150-μm demolding agent was applied to a die and the molten metal temperature was set to 710° C. in the gravity die casting. As described with reference to FIG. 6C, the casting time was 80 seconds.

Test 02: The molten metal temperature was decreased to 700° C., but other conditions were the same as those of the test 01. The casting time was 60 seconds.

Test 03: A 20-μm powder demolding agent was electrostatically sprayed to a die and the molten metal temperature was set to 700° C. in the casting method utilizing the electromagnetic pump. As described with reference to FIG. 7C, the casting time was 45 seconds.

Test 04: The molten metal temperature was decreased to 680° C., but other conditions were the same as those of the test 03. The casting time was 41 seconds.

Test 05: The molten metal temperature was decreased to 670° C., but other conditions were the same as those of the test 03. The casting time was 39 seconds.

Test 06: The molten metal temperature was decreased to 660° C., but other conditions were the same as those of the test 03. The casting time was 37 seconds.

Test 07: The molten metal temperature was decreased to 635° C., but other conditions were the same as those of the test 03. The casting time was 32 seconds.

(2) What was Obtained from the Tests:

According to the conventional technology (tests 01 and 02), the casting time was 60 to 80 seconds, but according to the present disclosure (tests 03 to 07), the casting time became 32 to 45 seconds, and the casting time became substantially half.

(3) Mechanical Test

A test piece cut out from the cast obtained by the test 01 was taken as a “test piece 1”, and mechanical characteristics were checked. Moreover, a test piece cut out from the cast obtained by the test 07 was taken as a “test piece 2”, and mechanical characteristics were checked.

(3-1) Mechanical Characteristics of Test Piece 1

Secondary dendrite arm spacing: 25 to 35 μm

Tensile strength: 290 MPa

0.2% proof stress: 210 MPa

Breaking elongation: 13.7%

10⁷-times fatigue limit: 62.2 MPa

(3-2) Mechanical Characteristics of Test Piece 2

Secondary dendrite arm spacing: 8 to 25 μm

Tensile strength: 312 MPa

0.2% proof stress: 238 MPa

Breaking elongation: 12.2%

10⁷-times fatigue limit: 75.7 MPa

(3-3) Evaluation

A secondary dendrite arm spacing (DASII) is the length of a branch elongated from a crystal. The shorter the branch is, the stronger a cast becomes.

The test piece 2 by the die casting method utilizing the electromagnetic pump had all of the DASII, the tensile strength, the proof stress, the breaking elongation, and the fatigue limit that were better than those of the test piece 1 by the gravity die casting.

As illustrated in FIG. 8, the obtained knuckle cast 40 is cut along the boundary line 64.

As illustrated in FIG. 9, the product portion 46 and the non-product portion 47 are separated from each other. The product portion 46 is finished as a knuckle by machining. The non-product portion 47 is taken as a scrap, is remelted, and is provided for the next casting process.

According to the present disclosure, it is one of the requirements to change the demolding agent 134 as described with reference to FIG. 6B into the thin powder demolding agent 65 as described with reference to FIG. 7B.

Moreover, according to the present disclosure, the temperature of each portion of the die 50 is set within a range that is between 120° C. to 240° C. immediately before pouring as described with reference to FIG. 7C. The temperature range was extensible to a range that is between 110° C. to 250° C. when examined together with the other tests.

Furthermore, the casting time in the above-described test 05 was 39 seconds, the casting time in the test 06 was 37 seconds, and the casting time in the test 07 was 32 seconds.

When 40 seconds that is the half of 80 seconds which was the casting time in the above-described test 01 is taken as an aiming casting time of the present disclosure, the tests 05 to 07 achieved such aim.

The molten metal temperature in the test 05 was 670° C. Since the liquidus-line temperature is 615° C., the molten metal temperature in the test 05 was (the liquidus-line temperature+55° C.).

The molten metal temperature in the test 06 was 660° C. Since the liquidus-line temperature is 615° C., the molten metal temperature in the test 06 was (the liquidus-line temperature+45° C.).

The molten metal temperature in the test 07 was 635° C. Since the liquidus-line temperature is 615° C., the molten metal temperature in the test 07 was (the liquidus-line temperature+20° C.).

When the molten metal temperature is a temperature that is the liquidus-line temperature to which 20° C. to 55° C. is added, reduction of the casting time by half is expected, and thus the productivity can be remarkably improved.

Note that the inventors of the present disclosure also examined AC2B (the liquidus-line temperature of 595° C.), and ADC12 (the liquidus-line temperature of 580° C.), and when the molten metal temperature was a temperature that was the liquidus-line temperature to which 20° C. to 55° C. was added, the casting time was reduced by half for those samples.

As described above, the present disclosure can be summarized as follows.

In the aluminum casting method of pouring an aluminum molten metal pumped up by an electromagnetic pump into a die, the thickness of a powder demolding agent which is applied to the die is set so as to be thinner than the thickness of a demolding agent applied in the gravity die casting, the temperature of the above-described die immediately before pouring is controlled so as to be within the range that is between 110° C. to 250° C., and the temperature of the above-described molten metal at the time of pouring is controlled to be a value obtained by adding 20° C. to 55° C. to the liquidus-line temperature of aluminum.

The electromagnetic pump is a mechanism that pours the molten metal into the die at low pressure.

Since the powder demolding agent that is thinner than the thickness of a demolding agent in the case of the gravity die casting is adopted, the temperature of the molten metal is decreased in comparison with conventional technologies, and the temperature of the die is also decreased in comparison with conventional technologies, the casting time can be reduced by half in comparison with that of conventional technologies. This enables the improvement of the productivity.

Hence, according to the present disclosure, there is provided the casting method that can improve the productivity without making a molten metal at high pressure.

Note that the method of the present disclosure is suitable for the casting process of a knuckle that has a complicated structure, but the cast is not limited to such a knuckle, and is optional as appropriate.

Moreover, when the casting time is to be managed at 40 seconds or less than that, in the case of the above-described test 05, there is a leeway in time that is one second. Since the surrounding temperature of the die changes depending on seasons and daytime or nighttime, it is desirable to set the leeway in time to be 3 seconds or so. In the case of the test 06 and the test 07, the leeway in time became equal to or greater than 3 seconds.

In the test 06, the temperature of the above-described molten metal at the time of pouring was controlled to be a value obtained by adding 45° C. to the liquidus-line temperature of aluminum.

In the test 07, the temperature of the above-described molten metal at the time of pouring was controlled to be a value obtained by adding 20° C. to the liquidus-line temperature of aluminum.

Meanwhile, in the case of FIG. 17, conventionally, the molten metal 127 was poured into the die 120 by the gravity die casting or by the low-pressure die casting.

In the case of the casting method utilizing the electromagnetic pump, the fluidity of the molten metal 127 increases in comparison with the gravity die casting or the low-pressure die casting. When the fluidity increases, a phenomenon equivalent to a phenomenon such that the flow speed increases occurs. That is, the faster the flow speed is, the more the occurrence of vortex and the turbulence become remarkable. Hence, in comparison with the gravity die casting or the low-pressure die casting, any devisal for the turbulence of the molten metal flow is highly required in the case of the casting method utilizing the electromagnetic pump.

As a devisal, the conical portion 57 illustrated in FIG. 5 is effective. That is, the conical portion 57 accomplishes remarkable effects in the casting method utilizing the electromagnetic pump in comparison with the gravity die casting or the low-pressure die casting.

In view of the foregoing, the method according to the present disclosure can be summarized as follows.

The molten metal 12 illustrated in FIG. 5 is pumped up by the electromagnetic pump (see FIG. 1, reference numeral 20), is supplied to the main sprue runner 59 from the pouring gate 58, is branched to the first sprue runner 61 and to the second sprue runner 62 along the conical surface 57 b of the conical portion 57. The molten metal that passes through the first sprue runner 61 is poured into the first cavity 53, and the molten metal that passes through the second sprue runner 62 is poured into the second cavity 54.

The fluidity of the molten metal is increased by the electromagnetic pump (see FIG. 1, reference numeral 20). Since the molten metal reaches the end portion of the cavity in a well manner when the fluidity of the molten metal is high, the molten metal temperature and the die temperature can be decreased. When the molten metal temperature and the die temperature are decreased, a solidification time of the molten is reduced, and thus the productivity can be further increased.

Note that the number of the first sprue runner 61, etc., branched from the main sprue runner 59 is three in the embodiment, but it may be two or equal to or greater than four, may be a multiple number, and such number is optional.

Moreover, even if a sprue runner spreads in a disk shape from the main sprue runner 59, since such a disk-shape sprue runner includes the first sprue runner and the second sprue runner in a cross-sectional view, this structure also falls in the scope of the present disclosure.

Moreover, the bottom of the conical portion 57 according to the present disclosure may be any one of a precise circle, an ellipse, an elongated circle, and a distorted circle. Furthermore, a polygonal pyramid, such as triangular pyramid or quadrangular pyramid, is not desirable because an edge line may cause turbulence. In the case of a polygonal pyramid that has a rounded edge line, however, such a structure is also involved in the conical portion 57.

Accordingly, the conical portion 57 is not limited to a precise circular cone in a narrow sense.

Meanwhile, when the molten metal 12 contains gas, such gas remains in the cast 35 in the form of pores. The pores are as a casting defect which is not desirable.

Accordingly, it is desirable to perform degassing also for the die 50.

It is recommended to locally provide a “clearance” in the die 50 for degassing. When, however, a clearance is large, although the degassing performance is well, some molten metal enters such clearances, making a burr. Conversely, when the clearance is small, the occurrence of a burr can be suppressed, but the degassing performance decreases.

In addition, since the adaptation of the electromagnetic pump 20 increases the fluidity of the molten metal 12, it is necessary to sufficiently analyze the setting of such a clearance.

Accordingly, the dimension of a clearance for degassing was examined by tests.

(4) Test Condition

(4-1) Casting method: Gravity die casting, low-pressure die casting, or casting method utilizing electromagnetic pump.

(4-2) Setting of clearance for degassing: 0.01 mm (10 μm) to 0.2 mm (200 μm).

(4-3) What was checked by tests: Presence or absence of burr, and degassing performance.

Test 11: The gravity die casting or the low-pressure die casting was adopted, and the clearance for degassing that was 0.2 mm (200 μm) was tested. When the clearance for degassing was 0.2 mm, no burr was produced, and the degassing performance was well. Hence, the evaluation is indicated by a circular symbol (that means good).

Test 12: The gravity die casting or the low-pressure die casting was adopted, and the clearance for degassing that was 0.1 mm (100 μm) was tested. When the clearance for degassing was 0.1 mm, the degassing performance slightly decreased. Hence, the evaluation is indicated by a cross symbol (that means bad).

Test 13: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.2 mm (200 μm) was tested. Since the fluidity of the molten metal increased by the electromagnetic pump, when the clearance for degassing was 0.2 mm, a large amount of burr was produced. Hence, the evaluation is indicated by a cross symbol.

Test 14: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.1 mm (100 μm) was tested. When the clearance for degassing was 0.1 mm, a little amount of burr was produced. Hence, the evaluation is indicated by a cross symbol.

Test 15: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.08 mm (80 μm) was tested. When the clearance for degassing was 0.08 mm, no production of burr was observed. Hence, the evaluation is indicated by a circular symbol.

It is found that when the clearance is equal to or smaller than 0.08 mm (80 μm), even if the electromagnetic pump is applied, the problem of burr is addressed. However, the smaller the clearance is, the more the degassing performance decreases. In order to further check this matter, the tests were further carried out.

Test 16: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.05 mm (50 μm) was tested. Since the degassing performance was maintained, the evaluation is indicated by a circular symbol.

Test 17: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.03 mm (30 μm) was tested. Since the degassing performance was maintained, the evaluation is indicated by a circular symbol.

Test 18: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.02 mm (20 μm). The degassing performance slightly decreased. Hence, the evaluation is indicated by a cross symbol.

Test 19: The casting method utilizing the electromagnetic pump was adopted, and the clearance for degassing that was 0.01 mm (10 μm) was tested. The degassing performance further decreased. Hence, the evaluation is indicated by a cross.

In view of the foregoing, according to the casting method utilizing the electromagnetic pump, it becomes clear that the suitable clearance for degassing is between 0.03 mm (30 μm) to 0.08 mm (80 μm).

A specific example to which the clearance with the above-described dimension is adopted will be described below.

A degassing portion 70 to be described below is fitted in the die 50 of the present disclosure.

As illustrated in FIG. 10, the movable die 52 that is a component of the die 50 is provided with degassing portion catching recesses 68 that are opened in the cavity 67, and through-holes 69 that extend from the respective degassing portion catching recesses 68 to the exterior of the die. The through-hole 69 has a diameter sufficiently smaller than that of the degassing portion catching recess 68. Each degassing portion 70 is fitted in each degassing portion catching recess 68. The degassing portion 70 is already fitted in the degassing portion catching recess 68 at the right side in the figure.

As illustrated in FIG. 11, each degassing portion 70 is a hollow body that includes, for example, a cylindrical body 72 which has a bottom portion 71, and a lid 73 that closes the opened end of the cylindrical body 72. The lid 73 is fastened to the cylindrical body 72 by swaging, screwing, or welding, etc. The degassing portion 70 is formed of tough carbon steel.

A hole 74 in communication with the through-hole (see FIG. 10, reference numeral 69) is formed in the lid 73. Moreover, vent holes 75 are formed in the bottom portion 71.

A gas that enters in the cylindrical body 72 through the vent holes 75 passes through the hole 74, and reaches the through-hole (see FIG. 10, reference numeral 69).

Note that the degassing portion 70 may include the cylindrical body 72 alone that has the bottom portion 71 without the lid 73.

As illustrated in FIG. 12, the vent holes 75 are each a thin and elongated slot with a width W that is between 30 μm to 80 μm, and multiple (e.g., three) such slits are provided in the bottom portion 71 so as to be in parallel with each other. The slit can be easily formed by a wire discharging and processing machine.

Note that as illustrated in FIG. 13A, the vent holes 75 may be slits arranged radially.

Moreover, as illustrated in FIG. 13B, the vent holes 75 may be replaced with a large number of fine circular holes 76. In this case, the diameter of each fine circular hole 76 is set to be 30 μm to 80 μm. However, since the fine circular holes 76 are a large number, the processing time increases. Conversely, the slit can be considered as a hole that is a collection of the fine circular holes 76. In view of the processing costs, the slit is better than the fine circular hole 76.

A molten metal 13 of aluminum pumped up by the electromagnetic pump 20 illustrated in FIG. 1 passes through a molten metal guiding block 14, and is poured in the die 50. Air is filled in the cavity 67 illustrated in FIG. 10 immediately before the pouring. The air is repelled by the molten metal 13 during the pouring. When repelled, the air passes through the degassing portions 70 and is discharged through the through-holes 69.

The cavity 67 is then filled with the molten metal 13 instead of the air. When filled, the molten metal 13 contacts the respective bottom portions 71 each illustrated in FIG. 12. As already described, the vent holes 75 each having a dimension that is between 30 μm to 80 μm does not allow the molten metal 13 to pass therethrough. The vent holes 75 with the dimension that is between 30 μm to 80 μm allows only gas like air to pass therethrough. Consequently, generation of burr is suppressed.

Each degassing portion 70 that has such features can be also utilized as a product extrusion pin. A specific example will be described with reference to FIG. 14.

As illustrated in FIG. 14, each cylindrical body 72 is sufficiently elongated so as to pass completely through the movable die 52 in the vertical direction. Moreover, a flange 81 is provided at the upper end (a portion sufficiently apart from the bottom portion 71) of each cylindrical body 72.

The flange 81 is held between an upper ejector plate 82 and a lower ejector plate 83.

A guide rod 84 is extended from the lower ejector plate 83, and is fitted in the movable die 52.

An arch shape frame 85 is mounted on the movable die 52, an ejector driving mechanism 86 is hung down from the arch shape frame 85, and the ejector driving mechanism 86 is coupled to the upper ejector plate 82. The ejector driving mechanism 86 may be any of a pneumatic cylinder, a hydraulic cylinder, and an electric-motor cylinder.

The lower ejector plate 83 is pushed upwardly by a compression spring 87, and its upward movement position is defined by a stopper 88 provided on the arch shape frame 85.

Air in the cavity 67 is discharged from the degassing portions 70, and the cavity 67 is instead filled with a molten metal. When the molten metal solidifies, the movable die 52 is moved up. Next, the upper ejector plate 82 and the lower ejector plate 83 are moved down by the ejector driving mechanism 86. This causes the degassing portions 70 to protrude into the cavity 67. The cast is removed from the movable die 52 by such protrusion.

Next, the upper ejector plate 82 and the lower ejector plate 83 are moved up by the ejector driving mechanism 86. Hence, it returns to the state illustrated in FIG. 14.

The cylindrical bodies 72 (the degassing portions 70) also serve as product extrusion pins. Since each cylindrical body 72 (each degassing portion 70) accomplishes both the degassing action and the product extrusion action, the added value increases.

Note that each degassing portion 70 may be provided integrally with the movable die 52. However, since the vent holes 75 are fine holes, the degassing portion 70 separate from the movable 52 like the embodiment facilitates the processing.

INDUSTRIAL APPLICABILITY

The present disclosure is suitable for an aluminum casting method for pouring an aluminum molten metal pumped up by an electromagnetic pump into a die, and a die that is utilized for the casting method.

REFERENCE SIGNS LIST

-   -   12 Molten metal     -   20 Electromagnetic pump     -   35 Casting     -   36 Center portion     -   40 Knuckle cast     -   41 Axle portion     -   42 First projecting portion     -   43 Second projecting portion     -   45 Axle hole     -   50 Die     -   53 First cavity     -   54 Second cavity     -   56 Column portion     -   57 Conical portion     -   57 a Vertex     -   57 b Conical surface     -   58 Pouring gate     -   59 Main sprue runner     -   61 First sprue runner     -   62 Second sprue runner     -   65 Powder demolding agent according to the present disclosure     -   67 Cavity     -   70 Degassing portion     -   71 Bottom portion     -   72 Cylindrical body     -   75 Vent hole     -   134 Demolding agent according to gravity die casting 

1-2. (canceled)
 3. A die utilized for an aluminum casting of pouring an aluminum molten metal pumped up by an electromagnetic pump into the die, wherein a thickness of a powder demolding agent applied to the die is set to be thinner than a demolding agent for a gravity die casting, wherein a temperature of the die immediately before the molten metal is poured is controlled so as to fall within a range that is between 110° C. to 250° C., and wherein a temperature of the molten metal when poured is controlled to be a value obtained by adding 20° C. to 55° C. to a liquidus-line temperature of the aluminum, the die being for casting a cast that comprises: a center portion; a first projecting portion projecting from the center portion; and a second projection portion projecting from the center portion in an opposite direction to the first projecting portion, the die comprising: a pouring gate provided at a bottom surface; a main sprue runner extended upright from the pouring gate; a first sprue runner branched from the main sprue runner; a first cavity to which a molten metal is supplied from the first sprue runner, and which forms the first projection portion; a second sprue runner branched from the main sprue runner; a second cavity to which the molten metal is supplied from the second sprue runner and which forms the second projecting portion; a column portion that is extended so as to go through the first cavity and the second cavity; and a conical portion which is connected to a tip of the column portion and which has a vertex, wherein an outer diameter of a bottom surface off the conical portion and an outer diameter of a tip surface of the column portion are designed so as to be consistent with each other, wherein the molten metal that passes through the main sprue runner is divided into, at the vertex, the first sprue runner and the second sprue runner along a conical surface of the conical portion and the column portion, and wherein: the cast is a knuckle; the center portion is an axle portion provided with an axle hole; and the axle hole is formed by the column portion in the casting.
 4. The die according to claim 3, the die comprising a degassing portion to discharge a gas remaining in a cavity, wherein the degassing portion is provided with a vent hole with a dimension that is between 30 μm to 80 μm.
 5. The die according to claim 4, wherein: the degassing portion is a cylindrical body fitted in the die; the cylindrical body comprises a bottom portion that faces the cavity; and the bottom portion is provided with the vent hole.
 6. The die according to claim 5, wherein the vent hole is a slit with a width that is between 30 μm to 80 μm.
 7. The die according to claim 6, wherein a plurality of the slits is provided in the bottom portion so as to be in parallel with each other.
 8. The die according to claim 5, wherein the cylindrical body also serves as a product extrusion pin to separate a cast from the die. 